Mobile data transmission and data services are constantly making progress. With the increasing penetration of such services, a need for increased bandwidth for conveying the data is emerging. In hitherto known scenarios, networks operated on reserved bands (licensed bands) within the available spectrum, which were reserved for the particular network. As licensed band operation has been increasingly utilized, portions of the radio spectrum that remain available have become limited. Thus, operators, service providers, communication device manufacturers, and communication system manufacturers, are all seeking efficient solutions to utilize unlicensed shared band operation. Communication on an unlicensed shared band is generally based on sharing an available channel between different communication devices. The different communication devices may utilize a common radio access technology (RAT). However, in certain scenarios, the different communication devices may utilize different RATs. In an unlicensed shared band, channel access can be distributed, where communication devices can detect a channel, and utilize a channel reservation scheme known to other communication devices in order to reserve a right to access the channel. In distributed channel access, a transmitting communication device and a receiving communication device are generally not synchronized to a global reference.
Currently, a system known as Long Term Evolution, LTE, is being further developed. When the LTE system concept is further extended in a way that it can be deployed also on unlicensed bands, the devices and local access points (APs) have potentially more spectrum available. That spectrum is to be used opportunistically as explained above. This setting can be considered as a kind of non-contiguous carrier aggregation, in which unlicensed spectrum is used as resources or “ground” for secondary carriers/cells for the licensed spectrum primary and secondary carriers/cells, controlled by the network transceiver station (or access node) known as Evolved Node_B, eNB. One step further would be to deploy an eNB totally on some shared band, like in television white space TVWS or in the industrial, scientific and medical, ISM, band without any anchor in licensed spectrum (in EUTRAN level) (Evolved Universal Terrestrial Radio Access Network) similar to WLAN deployments to make LTE an alternative solution against widely adopted IEEE technologies.
As a future LTE-A system may be deployed on unlicensed bands (e.g. TVWS or ISM bands), such environment sets further requirements/challenges for the system to operate appropriately.
In particular, the dynamic interference environment is very peculiar to the shared bands such as ISM (Industrial, Scientific, Medical) and Television White Spaces (TV WS). The quality of the communication link may change quite rapidly due to an unknown interferer (e.g. another system's device or devices occupying the band) or if the incumbent user decides to deploy the channel. Although the Quality of Service (QoS) cannot be guaranteed on the shared bands where the available resource is shared between secondary users, the service continuity should be protected in case of a sudden degradation of the signal quality or if the used channel becomes occupied. Especially the re-establishment of control channels on secondary channels is crucial in order to guarantee the service continuity on shared bands.
In one approach, secondary communication channels of an unlicensed band are e.g. derived based on GPS information for direct communication between communication devices without network node(s) being involved.
Thus, there is still a need to further improve such systems, in particular it is crucial to have reliable control channels so as to maintain and enable control of the system.